Wireless communication devices, such as cell phones and two-way radios, are becoming ever more popular. Such devices typically receive and transmit radio frequency (RF)signals from and to remote RF signal transmission towers, such as cell towers. While RF signals are capable of penetrating solid objects, the strength and quality of those signals degrade as more barriers are present between the transmission tower and the wireless communication device. Signal degradation is especially acute within structures, such as office buildings or factories, which offer multiple barriers between the transmission tower and the wireless communication device.
In-building radio frequency communications systems have been developed to improve performance of wireless communication devices within structures. These systems typically use a strategically located and directed antenna, which typically is located on the exterior of the structure (roof or side wall), providing a communications link with a RF signal transmission tower. The directed antenna is focused at a specific RF signal transmission tower (primary RF signal donor site) in an effort to maximize desired signal levels from the donor site to the in-building system. In addition, the directed antenna will minimize the level of non-desired and interference producing signals that arrive at angles, relative to the direction that the external antenna is focused, outside the horizontal beamwidth of the external antenna. The desired effect of the directed antenna is to isolate the in-building system from all RF signals other than those used at the primary donor site. They also use one or more low profile antennas located within the interior of the structure, strategically placed to provide coverage in areas where the RF signal levels and/or quality are not adequate to support reliable transmissions. The internal antennas are linked together by an infrastructure comprised of coaxial fiber optic and/or network cables and power splitters. The infrastructure is typically connected with the external antenna through a bi-directional amplifier (BDA), a device that increases the strength of the signal passing through it, either as the signal is received from the transmission tower to be transmitted to the wireless communication device (the signal downlink) or as the signal is received from the wireless communication device to be transmitted to the transmission tower (the signal uplink). In such a system, the RF signals are 1) received from the transmission tower by the external antenna and connected to the BDA; 2) amplified by the BDA; 3) distributed via the system infra-structure to the internal antennas, whose quantity and location inside the facility are appropriate to meet system requirements; and 4) radiated at a sufficient level to support reliable radio communications. The net effect is to allow the signals to pass between the transmission tower and the external antenna and between the wireless communication device and the internal antennas with relatively few intervening barriers. This minimization of intervening barriers, together with the signal amplification provided by the BDA greatly improves in-building performance of wireless communication devices.
In-building radio frequency communications systems are well known in the prior art, and may be implemented in any number of ways. See, e.g., Point-To-Multipoint Digital Radio Frequency Transport, U.S. Pat. No. 6,704,545 (Wala), issued Mar. 9, 2004; Communication System Comprising An Active-Antenna Repeater, U.S. Pat. No. 5,832,365 (Chen, et al.), issued Nov. 3, 1998; Method Of Locating A Mobile Station In A Mobile Telephone, U.S. Pat. No. 5,634,193 (Ghisler), issued May 27, 1997. However, while these systems are designed to handle the communications within a building, they all depend on reliable signals from the radio frequency transmission tower to support in-building transmissions. Thus, in-building signal enhancement tends to be susceptible to failure if there is an interruption or degradation of service at the external radio frequency transmission tower. This may result from a mechanical failure, a planned maintenance shutdown, environmental factors such as a lightning strike, or other causes, most of which are beyond the control or even awareness of the end use of the wireless communications device. In-building radio frequency communications systems known in the prior art are unable to recover from such interruptions and thus fail to provide the level of quality and reliability desired by end users.
One class of in-building frequency communications system known in the art does exemplify some failure recovery properties. Where an omni-directional antenna is used as the external antenna for an in-building system, by design the omni-directional antenna sends and receives RF signals equally in the horizontal plane, compared to a directional antenna, which will focus RF energy from approximately 15° to 100° of the horizontal plane. When an omni-directional antenna is used as the external antenna for an in-building system, there may be some degree of radio frequency transmission site diversity due to the inherent ability of the omni-directional antenna to transmit/receive RF signals equally in the horizontal plane. Under this scenario, signals from more than one radio frequency transmission tower may be connected into the in-building system and if signals from one radio frequency transmission tower fail, signals from a different radio frequency tower may be available to provide a level of coverage inside the facility. However, this configuration does not allow for specific redirection for precise control over alternative RF signal sources. The present invention, by placing such control with the system designer, is an improvement over in-building systems that have been designed to provide radio frequency transmission tower diversity through the use of an omni-directional external antenna.
The present invention is directed to an in-building radio frequency communications system with the capability to automatically transfer RF signals to the in-building system from multiple radio frequency transmission towers. As such, it offers improved RF signal access reliability over known systems.
It is an object of this invention to provide a fault tolerant in-building radio frequency communications system which minimizes disruptions due to failure of the RF signals from the primary radio frequency transmission tower.
It is a further object of this invention to provide a donor site diversity system which continuously detects the strength and quality of RF signals from a primary radio frequency transmission tower in order to automatically switch an in-building radio frequency communications system to an ancillary radio frequency transmission tower whenever the strength and quality of RF signals from a primary radio frequency transmission tower fall below an acceptable threshold. Other objects of this invention will be apparent to those skilled in the art from the description and claims which follow.